The invention relates to rotor laminae assemblies for cast rotors used in the manufacture of dynamoelectric machines and more particularly it relates to such a rotor having radial cooling ducts connected to axial coolant passageways through the rotor assembly in a manner that enables rotor conductors to be cast in conductor slots of the assembly without impairing the cooling ducts or axial coolant passageways. The invention also makes it possible to cast the conductors of a rotor assembly without requiring the use of spacer pins, or spot welded collar sub-assemblies, separately inserted into the laminae assembly of the rotor during a casting operation to prevent the flow of casting metal from the conductor slots into cooling ducts of the assembly.
Prior to the present invention it was common practice to cast conductors in laminated rotor assemblies for dynamoelectric machines by utilizing various types of spacers to prevent molten metal from entering the rotor air ducts during the casting operation. For example, U.S. Pat. No. 2,368,296 discloses a method of forming radial ventilating passages in a cast rotor in which ring-shaped spacers are inserted between groups of laminations during the casting operation. After such a casting operation the rotor assembly is further treated to melt or dissolve the temporary spacers so they are easily removed from the rotor. In that patent the use of tin alloy, plaster or clay with a dissolvable binder is suggested for the ring-shaped spacers. The same inventor discloses in U.S. Pat. No 2,368,295 the use of cardboard or similar combustible material to form spacers in a rotor lamination during a casting operation. Similarly, in U.S. Pat. No. 2,607,968 there is described a method for casting dynamoelectric machine rotors with air ducts which are formed by spacers made of reinforced plaster material between the lamination sections of the rotor during a casting operation. Following the casting procedure, the plaster material is disintegrated by contacting it with water to wash the spacers from the air ducts.
Although the use of such dissolvable or frangible spacer materials is well-known, it is more common practice in the manufacture of relatively large dynamoelectric machine rotors to place a plurality of removable steel pins, or spot welded collar sub-assemblies, between sections of the rotor laminations to form the desired cooling ducts in the rotors. The use of such a reusable spacer procedure is shown, for example, in U.S. Pat. No. 2,504,824.
While the utilization of metal pins to form air ducts in cast rotors has become a preferred practice in the manufacture of dynamoelectric machines, relative to the use of frangible or dissolvable spacing members to form the cooling ducts, it has long been recognized that this method inherently has several disadvantages. In practicing this method it is necessary to utilize a relatively large number of individually placed steel pins to form the cooling ducts in a given rotor. Typically, the number of such pins will be around 1,000 for a medium size rotor, i.e., a rotor about 3 feet in length and 2 feet in diameter. Since these pins must be individually positioned in the rotor as its lamination assembly is built up prior to a casting operation, and since the pins must subsequently be individually extracted from between the laminations following the casting operation, the labor cost involved in this method is substantial. In addition to the installation and removal of the pins, care must be taken to carefully clean the pins between each use to assure their close precision fit in subsequent casting operations so that molten metal does not flow between them and the adjacent rotor laminations. Moreover, the normal use and handling of such pins inevitably results in mechanical abuse and wear that necessitates frequent replacement of the pins. Of course, such replacement costs are a substantial manufacturing expense that it would be desirable to avoid, if possible.
Well before the development and commercialization of such removable ring or pin techniques for casting conductors in laminated rotors, it was known to fabricate laminated rotors of a series of differently punched laminae arranged to form axial coolant passageways connected to radial coolant ducts by venting channels. An example of several early configurations of that type of ventilating arrangement in a wound rotor structure is shown in U.S. Pat. No 890,577 which issued on June 9, 1908. However, since such early rotor cooling arrangements were not suitable for use in manufacturing cast conductor rotors, due to the fact that they would allow molten conductor metal to enter the coolant passageways therein, it remains common practice to manufacture rotors having cast conductors by the aforementioned movable spacer-pin methods.
In more recent times, as shown in U.S. Pat. No. 3,684,906, which issued on Aug. 15, 1972 to one of the applicants named herein, a relatively small castable rotor for regfrigerant compressor motors was disclosed in which a plurality of sets of differently configured rotor laminae were arranged to form tortuous paths through the rotor from arcuately spaced axial refrigerant-carrying passageways, through intermediate vent passageways, to arcuately disposed radial ducts. Such small refrigerant compressor motors are distinguished from the present invention by requiring the use of radial coolant ducts in two different sets of laminations so that the radial ducts in either such set do not extend the full depth of the adjacent conductor slots. Furthermore, the flow-restricting nature of the small, tortuous ducts used to carry refrigerant through such rotors are not suitable for use as coolant passageways for larger air-cooled rotors in which large volumes of air must be moved through the rotor ducts with little pressure loss.